The United States is in the midst of a serious public health problem pertaining to the arrest and incarceration of individuals with serious mental illnesses, in conjunction with an inadequacy of mental health treatment in criminal justice settings. This application aims to examine the role of variability in availability of/access to menal health services as they relate to the widely implemented Crisis Intervention Team (CIT) model of collaboration between law enforcement and mental health. CIT can be considered a form of pre- booking jail diversion that facilitates referral to the mental health services system. While some arrangements with mental health services (such as a no-refusal policy and priority to police-referred individuals) exist across cities and states (these being among the core elements of the CIT model), they often differ in the services provided, and most are limited to emergency treatment and stabilization of acute cases. The proposed research will address a critical knowledge gap in mental health intervention and services research, as little research has examined the role of mental health service accessibility on the effectiveness of CIT, especially in terms of safety, mental health service utilization and engagement, and criminal justice system involvement of individuals with serious mental illnesses. Differences in access and service availability will be examined across all 25 Chicago police districts. This research will address an open question of the extent to which greater access to mental health services is sufficient to reduce arrests when officers encounter individuals with mental illnesses, and the extent to which specialized training of officers adds to how effective that access is as a method of diversion. Methods such as cross-sectional assessments with police officers, baseline and longitudinal follow-up assessments with individuals who have serious mental illnesses and have had a recent encounter with law enforcement, and in-depth interviews with members of these two groups and other key informants, will be utilized to achieve the project's aims. The specific aims are to: (1) estimate the impact of CIT training on immediate outcomes of mental health-related calls (arrest, linkage to mental health services, or contact only) across police districts with varying service accessibility; (2) determine how these immediate outcomes, as well as CIT response, access arrangements, and availability of mental health services affect longer-term outcomes and utilization of services among individuals with mental illnesses over a period of 12 months; and (3) describe how accessible it is for officers to connect individuals with psychiatric services through both experiences that officers, consumers, and other key individuals have had and the perceptions they hold. A secondary aim will explore the connection between geographic location (via spatial mapping) and psychiatric service accessibility, characteristics of community, characteristics of calls received and subjects, immediate outcomes, and longer- term outcomes.